The present invention generally relates to box making machines and more particularly to novel and improved methods and apparatus for resurfacing the anvil blanket of a rotary die cutter used to crease and/or cut corrugated boards in a box making machine.
Rotary die cutters include a die drum or cylinder having on its surface a cutting die typically made of steel rule for cutting or creasing corrugated board against an anvil drum or cylinder as the board passes between the two drums. The anvil cylinder has a blanket on its circumferential surface typically made of urethane usually provided in 0.30 inch thick and 10 inch to 20 inch wide segments for ease of rotation and replacement. When the anvil blanket develops an irregular surface and becomes cut-up due to repeated contact from the steel rule dies on the die drum, the operation of the rotary die cutter must be stopped together with the production run of the box making machine. A cutting tool such as a knife or a rotating mill tool or grinding wheel is then operated while moved along the length of the surface of the blanket to trim the blanket to even and smooth it. Approximately 0.010 to 0.020 inches is trimmed from the blanket surface. The diameter of the blanket is then measured, and a speed compensator for the anvil is also adjusted since the diameter of the anvil has been reduced by the trimming operation. In this regard it is well known that the surface speed of the anvil affects the accuracy of the die cut in the corrugated board. Ideally the surface speed of the anvil should be equal to the speed of the board as it travels through the die cutter. However, due to the constant wear in the blanket surface, it is not possible to maintain a constant diameter of the blanket and nor is it practical to constantly stop production to trim the blankets, to measure the blanket diameter and adjust the speed compensator to change the speed of the anvil in accordance with its reduced diameter.
Prior methods have therefore resorted to trimming between 0.010 to 0.020 inches from the anvil blanket surface, at relatively large intervals of time in order to avoid constant shut down of the box making machine for resurfacing the anvil blanket. The result is that conventional rotary die cutters used in box making machines are subject to inaccurate die cuts or creases in the corrugated boards while shortening the life of the anvil blanket.
One of the objects of the present invention is to provide a novel and improved rotary die cutter for a box making machine which overcomes the above noted problems attending conventional rotary die cutters used in the box making industry today.
Another object of the present invention is to provide novel and improved methods and apparatus for resurfacing or trimming an anvil blanket of a rotary die cutter for box making machines to improve the accuracy and consistency of the cutting and creasing of the corrugated boards. Included herein are methods and apparatus for automatically adjusting the speed of the anvil to compensate for the surface material removed from the anvil during resurfacing.
A further object of the present invention is to provide such method and apparatus for trimming or resurfacing an anvil blanket of a rotary die cutter and for controlling an associated anvil speed compensator while the die cutter is operating during a production run thereby avoiding the need to shut down production.
A still further object of the present invention is to provide such method and apparatus for resurfacing or trimming a rotary die cutter which increase the life of the anvil blanket. Included herein are such method and apparatus which allow only a minimum amount of surface material preferably between 0.0005 to 0.002 inches to be trimmed from the anvil blanket as the blanket surface becomes irregular during use.
Yet another object of the present invention is to provide such method and apparatus which may be applied to conventional rotary die cutters for resurfacing or trimming their anvil blankets.
A rotary die cutter having a die drum and an anvil drum is provided with an abrader cylinder mounted alongside and generally coextensive with the anvil drum for rotation against the anvil blanket to trim the surface of the blanket. In operation the abrader cylinder is moved virtually continuously against the anvil blanket as the die cutter is operating on corrugated boards. The abrader cylinder rotates in the same rotatative direction as the anvil and has an abrasive surface which abrades or grinds the blanket surface to a smooth, even and level condition. A motor and encoder assembly is provided to drive the abrader cylinder towards or away from the anvil drum and to record the position and the amount of movement of the abrader cylinder which information is fed to a computer or programmable controller for calculating the diameter of the anvil blanket surface and the amount of speed change needed in the anvil to compensate for the change in diameter of the anvil blanket surface.